Research And Design Of A High Efficiency And High Step-up Ratio Converter Based On Boost Dc-dc

White LED is increasingly widely used in portable electronic devices. White LED Driver IC for LCD backlighting, which is the key component of the system, is the research focus in power management ICs. Because of the smaller size of portable electronic devices, the larger size of the backlit LCD screen and the higher requirement on the energy saving, White LED driver IC must have higher integration, step-up ratio and efficiency characteristics.In this thesis, with the in-depth study of current technique for white LED drivers, six main DC-DC driving methods and two LED driving modes are discussed. According to the application demands of this research, Boost DC-DC and LED series driving mode are chosen. Based on four key technical points the peripheral circuits and the overall frame of the chip are designed. Then, the main subcircuits such as bandgap reference(BGR), current detection, ramp compensation, oscillator, error amplifier, gate drive including synchronous rectifier and PWM comparator are implemented and simulated with SALICIDE ANALOG PROCESS WITH PLDD 0.35μm process. With a PTAT structure, BGR can supply any reference voltage and bias current. Current detection circuit could effectively resolve the problems of high power loss and difficult integration that exist in conventional current detection circuit. A new type of dynamic ramp compensation technology is used so that the compensation problems in peak current-mode of PWM modulation which based on Boost DC-DC can be solved. As the operation mode of the two comparators in the oscillator circuit is controlled by the switch, nearly 50% of the oscillator power consumption can be saved.Finally, the whole chip simulation results by HSPICE are given: in typical application condition, the start-up time of the chip is 700μs; the output voltage is 20V while the load current is 22.7mA, and the efficiency is above 85%. The chip can start up and operate normally when the supply voltage is 2V. The results show that the main characteristics of this chip matched the specification.